I am a film (35mm and large format) and digital APS-C shooter, and I am looking to upgrade (sidegrade?) to a full frame or preferably medium format digital system. There are various parts of the equation here, but what I am most interested in is lens performance normalized for the sensor size.

I am an engineer and I am driven by objective measurements. The problem is that I have not been able to find any good resource about medium format lenses on the internet. Everybody "knows" that MF lenses are sharper than Canon/Nikon lenses (are they?), and everybody "knows" that digital view camera lenses are the sharpest of all (are they really??), but I can't seem to find actual measurements that backs up this knowledge.

I am interested in tests done at landscape shooting apertures and varying distances. Wide open lens measurements are useless for the landscape photographer, and photographing flat subjects at a fixed distance is better than nothing, but ultimately not very illuminating either.

If this mythical website with all this information does not exist, I am mostly interested in how the Canon tilt-shifts mounted on GFX50 compare to other tilt-shift/view camera solutions in the 50Mpix range (sadly that's all I can afford), again, when normalized for the different sensor sizes. I am also intersted in the relative performance of the GFX and the (newish) Pentax MF lenses (including the zooms). Again, at landscape shooting shooting aperture.

Has anyone made such a comparison?

By the way, I hope to avoid subjective impressions about which lens is sharper, or other unquantifiable ideas such as all lenses being "sharp enough", or that all these MF/FF systems perform "the same" at usual print sizes, etc. The performance of the system is something you can measure, and I hope someone actually measured it!

Go to The Last Word, Jim Kasson's blog. He will give you what you are looking for. As a long time Large format user, the short answer is that you don't need medium format to equal in real terms what 8x10 gives in sharpness, acutance and the like. Digital has a very close connection from the image capture to the print, which film does not have: changes in processing, exposure mistakes, (brightness ranges difficulties), lack of perfection in enlarging, etc etc.Digital is a lazy man's answer to decent photography, and a really careful photographer can produce fantastic results with FF, never mind Medium Format.

In a nutshell, in terms of 'usable resolution' when viewed at the same final display size (in lp/ph, i.e. normalized for sensor size) and all else equal/equivalent, the larger format trumps the smaller one as a system in practice most of the time - it's just geometry.

On the other hand the smaller the format, the 'sharper' it often can be in practice as a system in the center (in lp/mm) - for a number of reasons you can imagine (typically smaller apertures and pixels being two of them). I don't own MF equipment or tilt/shift lenses but here is a comparison you may find interesting, with all its limitations (details with setups here):

Unless lenses have developed magical properties they did not have in film days, you face a problem: folks used to believe that if you went from a Pentax 135 format camera to a Pentax 6x7 camera, the lenses would be just as crisp across the entire 6x7 area as they were across the 135 area. They never were; the small lenses were more crisp because of the smaller area that they had to be designed to cover. Larger formats simply meant lesser magnification to reach a similar size of print, not the same lens crispness as smaller format lenses spread across a larger format.

I tested this out once with my own gear: Nikon and Hasselblad 500 Series. I took a whole Nikon negative and also a 'blad negative (6x6) where the image being tested was the same size as on the Nikon. The print from the Nikon was superior to the same-size section on the 'blad. Both were studio heads shot with umbrella flash. I used the 3.5/135mm Nikkor on the Nikon, and the 4/150mm Sonnar on the Hassy. The two formats I used were not really that dramatically different in actual size, so it would have been interesting to try the same experiment using the Nikon and then the same-size area from an 8"x10" film... I didn't have such a format of my own.

In a nutshell, in terms of 'usable resolution' when viewed at the same final display size (in lp/ph, i.e. normalized for sensor size) and all else equal/equivalent, the larger format trumps the smaller one as a system in practice most of the time - it's just geometry.

On the other hand the smaller the format, the 'sharper' it often can be in practice as a system in the center (in lp/mm) - for a number of reasons you can imagine (typically smaller apertures and pixels being two of them). I don't own MF equipment or tilt/shift lenses but here is a comparison you may find interesting, with all its limitations (details with setups here):

Jack

Looking at your numbers and logic ; may i conclude that because larger format lenses are less sharp than FF lenses:an image made with 50MP FF-camera may show more resolution than a 50MP MF-camera when printed the same size.

-Why are large format lenses less sharp than their smaller format counterparts?Is there an optical/physical boundary or an economical one ?

Looking at your numbers and logic ; may i conclude that because larger format lenses are less sharp than FF lenses:an image made with 50MP FF-camera may show more resolution than a 50MP MF-camera when printed the same size.

Hi Kers,

Not necessarily, there are many factors at play, including some that have nothing to do with sensor and lens (for instance, less magnification may mean less vibration). With lenses it depends whether and how much they are less sharp. See for instance here.

Why are large format lenses less sharp than their smaller format counterparts?Is there an optical/physical boundary or an economical one ?

You know why a lens is usually not at at its best wide open and it improves substantially when stopped down a couple of stops? The main reason is that in the second case closing the aperture cuts out a large portion of the pupil, effectively only using a small portion of the glass at the center of the lens. Within reason, smaller means easier to control and manufacture to high tolerances.

Hi Jack, thanks for the article. Actually, I have read all your articles. Exactly what I have thought.

It seems that MTF measurement using backlit razors is very simple and very effective. I wonder why is it not ubiquitous. It seems to me that because of super sampling even the sensor doesn't matter much (up to a reasonable degree, plus, you need a sensor large enough if you want to test the corners of every lens), so in principle you can test any lens with the same sensor, provided you have the necessary adapters. Am I right?

It seems that MTF measurement using backlit razors is very simple and very effective. I wonder why is it not ubiquitous.

You are right, I think it is very useful though it requires a fair amount of fiddling. In practice the most time consuming portion of the procedure is properly aligning the target (razor or chart) and consistently nailing focus.

It seems to me that because of super sampling even the sensor doesn't matter much (up to a reasonable degree, plus, you need a sensor large enough if you want to test the corners of every lens), so in principle you can test any lens with the same sensor, provided you have the necessary adapters. Am I right?

You are correct about pitch - but the sensor matters because of pixel aperture, which acts like a low pass filter. The larger the aperture, the more the low pass function. So smaller pixels capture more detail and that is reflected in the measurements.

You can try to model all this and account for differences but I think unless you are prepared to invest a lot of time (and some money for equipment like a focus rail), for the typical amateur I think the slanted edge method has more relative than absolute value.